1. Field of the Invention
The present invention relates to a modified baculovirus and to its use for the production of immunoglobulins.
2. Description of Related Art
Antibodies or immunoglobulins are produced by B lymphocytes. Each B lymphocyte secretes a single type of antibody. Each immunoglobulin molecule is constituted of the combination of two heavy chains (H) and two light chains (L) connected by disulfide bridges. Each chain is constituted of a variable region (VH and VL) which contains the antigen attachment site and a constant region (CH and CL). There are many types of heavy chains (γ1, γ2, γ3, γ4, α, ε, μ) which define the various classes of immunoglobulins (IgG1, IgG2, IgG3, IgG4, IgA, IgE, IgM . . . ) and two types of light chains: kappa chain (κ) and lambda chain (λ). For example, the IgG1 class antibodies are constituted of two heavy chains of the γ1 type and two kappa κ or lambda λ light chains. The variable regions are responsible for the specificity of the antibody for its antigen.
For each chain of a given antibody, the variable region has many domains, certain of which are preserved to varying degrees. The rearrangement of these variable regions is the result of a recombination at the level of the genomic DNA of the B lymphocytes.
Monoclonal antibodies are conventionally produced from cultures of hybridoma lines, with each line derived from a single B lymphocyte and secreting a single type of immunoglobulin.
Monoclonal antibodies (mAbs) are commonly used at present for in vitro diagnostics, and their use in therapy and for in vivo diagnostics shows promising developments. These developments, however, are held back by the fact that the only monoclonal antibodies that are relatively easily available in adequate quantities from hybridoma cultures are monoclonal antibodies from rodents. However, these rodent immunoglobulins (and nonhuman immunoglobulins in general) induce an undesirable immune response in humans which considerably limits their therapeutic value.
Extensive research has been carried out with the goal of obtaining immunoglobulins that do not have this drawback; specifically, it has been proposed to employ genetic engineering techniques to fabricate recombinant antibodies in which the largest possible part of the molecule is derived from a gene of human origin.
The resultant antibodies, in which only the variable domains are of non-human origin, are referred to as chimeric antibodies. There also exist antibodies referred to as human in which the sequences of the variable regions not directly involved in the recognition of the antigen have been replaced by sequences of human origin. In both cases, the greatest part of the immunoglobulin molecule is derived from a gene of human origin.
Nevertheless, the production of antibodies using genetic engineering requires the selection of a suitable host in order to ensure that the post-translational modifications required to reproduce the properties of the native antibody are made. For this purpose, it has been proposed, among other approaches, to employ the baculovirus/insect cell system.
Baculoviruses are widely used as vectors for the expression of heterologous genes, placed under the control of viral promoters, in the cells of infected insects. The promoter of the genes encoding polyhedrin or p10, proteins produced in large amounts during the late phase of the viral replication cycle, is thus frequently used for this purpose.
HASEMAN and CAPRA [Proc. Natl. Acad. Sci. USA, 87, 3942-3946 (1990)], PUTLITZ et al. [Bio/Technology, 8, 651-654 (1990)], and REIS et al. [Bio/Technology, 10, 910-912 (1992)] thus constructed baculoviruses in which were inserted at a single locus two copies of the polyhedrin promoter, with one of these copies controlling the expression of a gene coding for the heavy chain of a mouse immunoglobulin and the other copy controlling the expression of a gene coding for the light chain of the same immunoglobulin. The insect cells infected by these baculoviruses secreted immunoglobulins that had essentially the same properties as the antibodies of lymphocytic origin employed as the model. However, the structure of the baculoviruses modified in this manner is not maintained beyond several cycles of viral replication.